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Abstract

We report that it is possible to create a fiber electret by having both internal electrodes of a twin-hole fiber at the same anodic potential, i.e., without the use of a contacted cathode electrode. We find that a stronger and more temperature-stable charge distribution results when the fiber core is subjected to an external field near zero. Negative charges from the air surrounding the fiber are sufficient for the recording of an electric field across the core of the fiber that is twice stronger than when one anode and one cathode electrode are used. The enhancement in stability and in the strength of the effective χ(2) induced are a significant step towards the wider use of fibers with a second order optical nonlinearity.

Figures (5)

Charging circuit used to create an electret in an optical fiber, where both internal electrodes are at the same potential. The field recorded across the core becomes comparable to the breakdown field of silica. After electret creation, each electrode is connected to one pole of the bias supply and the fiber exhibits the linear electrooptical effect. The picture shows a SEM image of one of the 125-µm diameter fibers used. The white centre circle is the fiber core.

Fiber cross section after etching for 45 sec in HF. In (a), a single metal-filled electrode was used as anode, and the other hole was left empty. The fiber was charged for 33 min at 255 °C with 4.3 kV applied to the electrode. A circular depletion region is formed. In (b), both holes had electrodes connected to the same positive high voltage potential (4.3 kV). One depletion region is formed around each electrode, even if the potential difference between them is zero.

Phase shift induced in fiber as a function of voltage applied between the internal electrodes after the fiber has been charged with the set-up of Fig. 1. The phase shift is measured in π radians. The red curve is a parabolic fit to the data.

Isothermal annealing of poled (red) and charged (blue) at 250 °C on a linear time scale. The remaining electrooptical coefficient was measured after each erasure period from a parabolic fit as shown in Fig. 3.

Top row: equipotential map of fiber subjected to a charging voltage 5 kV applied to both internal electrodes assuming electrically grounded outer surface. Initially, the potential drop across the core is small (a), but grows as poling progresses (b). Bottom row: respective distribution of Na+ ions measured as 1021 ions/m3. The initial distribution of mobile ions is assumed to be uniform (c), and it evolves into a two-ring configuration (d).